Understanding the language of medicines use in older adults: a systematic review of definitions and measures

Background Many terms have been used in the literature to describe medicines use behaviour without standardized definitions. It is unclear whether these terms are being applied interchangeably and variably across different measurement methods. Aim To review the definitions of medicines adherence, compliance, persistence, and concordance in the published literature on older adults and identify how they have been measured. Methods A systematic literature search with review of reference lists was conducted. Two investigators independently reviewed the identified articles. A content analysis was conducted using NVivo V.14 to identify the main elements for defining medicines adherence, compliance, persistence, and concordance. Descriptive statistics were used to summarize the studies by their type, country of study, and related participant characteristics. Key findings One hundred and fifteen identified papers were eligible for inclusion. Discrepancies were found in the definitions of each term. Commonalities were found between the definitions of medicines compliance, adherence, and persistence. Only one study was found on medicines concordance. Similar instruments such as the medication possession ratio (MPR) and proportion of days covered (PDC) were used to determine medicines adherence, compliance, and persistence. Some measurement instruments were applied differently across studies in which different cut-off values were used to classify outcomes. Conclusions There is a considerable overlap and inconsistency in the definitions of terms used to describe medicines use behaviour. The imperative to standardize the definitions appears as a critical step to strengthen consistent measurement approaches leading to accurate estimates of medicines use outcomes.